Resettable fuse



Dec. 26, 1933. Y 1 E p LARSH 1,940,956

RESETTABLE FUSE Filed Feb. 6. 1932 fmsz//a//bf/ U- 7 Patented Dec. 1933 @UNITED STATES PATENT oFFlCaIE REsE'r'rABLE FUSE Everett P. -Larsh, Vandalia, Ohio, assignor to `The Master'Electric Company, Dayton, Ohio,

a oorporationrof Ohio Appiicatien The present invention relates to electric lfuses or thermally controlled circuit breakers, and more particularly to a resettable fuse which, after having been automatically operated under excessive temperature influence to open an electric circlosed, and having a fusible connection with the operating device, which when fused undere'xcessive heat condition releases the device for automaticrmovement out of contacting position underv inuence of the spring thereby opening the circuit.V The cooling of the-fusible material reunites the detent and operating device in the relation to Which they have been moved. 'Ihe subsequent manual return of theV contact device to `closed position` retensions the spring and readjusts the detent to hold the device in its closed condition until again released by subsequent fusing of the joint. The fusible joint may be subjected to direct heat radiation or may be subject i to heat iniiuence through a collector of heat conductive material, orV may be operated by the inuence of a heater coil normally included in the controlled circuit. l. y a

4The object of the inventionis to simplifyA the construction as Well as the means and mode of operation of such devices' whereby they Will not only be cheapened in construction; but will be ymore eiiicient in operation, automatic in action,A uniformly sensitive to thermal conditions, capable of repetitions operation, and unlikely-to get out of order. p

. A further object of the invention is to provide an automatic circuit breaker which Will aiord minimum resistance in, the circuit, and which will respond promptly and with decisive action to an excessive thermal condition.

A further object of the invention is to provide an automatic circuit breaker operable by external thermal conditions.

VA further object of the invention is to provide an automatic circuit breaker Which will be automatically reconditioned after use.

A further objection of the invention is to pron vide a simple device having few operating parts which may `be readjusted to operativeV condition repeatedly. v

` Withthe above primary and other incidental objects in `View as will more fully appear in the speciiication, the invention consists yor the feain its application to amotor housingwhere in the Februaryc, 1932. serial No. 591,403 i4 claims.l (c1. 20u-124) tures `oi" construction, theparts and combinations thereof, and the mode of operation, or their equiv- 'alents, as hereinafter described'and set forth in the claims. y

vReferring to the accompanying drawing Wherein arefshoivn the preferred, but obviously not the only forms of embodiment of the invention, Fig.

ll is a longitudinalsectional,View ofthe assembled resettable fuse forming the Subject matter hereof adaptedfor operation underexternal heat con- 65.

rditions. Fig. 2 is a transverse sectional view on line 2--2 oi Fig. l. Fig. 3`is a transverse' sectional View on line 3-3 of Fig. l. Fig.,4 is a longitudinal sectional view of the assembled resettable fuse embodied in a standard type oi fuse plug adapted for insertion in an electric circuit as a lprotection against overload. Figi 5shows a plan View. Fig. 6 discloses another modification wherein a ratchet clutch mechanism has been used instead of the friction clutch shown in Fig. 2. Like parts are indicated by similar characters of reference throughout the several views. f rThe fuse construction forming the subjectmat` ter hereof may be embodied in different forms andA applied to ,numerous purposes of v,which only two are herein shown vand described. y i The embodiment of the invention illustrated in Fig. l is'especially applicableto the control of anv electric circuit under influence Vof surroundingy temperature'conditions and has been illustrated.

event the motor should' be overheated topredetermined degree the device will operatevto open the motor circuit. `This is merely an illustrative p application `and it isvto be'understoodfthat the de-Kj 90 vice may be positioned in Aany Warm 'air stream or .in proximate relation to any point at which abnormal rise of temperature is likely to occur.v

In Fig. 4 the invention is embodied in asafety devicefor installation in a standard fuse block socket and isoperable by overload upon the electric circuit causing'the heating of a h eatercoil` embodied WithinA the device. VThe general conj structionv in both instances vis the same. Y n

AThe device as'illustrated in the drawing com` 100 prises a tubular shell `or casing of `dielectric material `having anv enlarged head 2 and provided with diametrically opposite slots 3 3 for `con' venience of assembly. Interiorly the casing orv shell' is formed With two oppositely disposed, 105 spaced rabbets or shoulders 4 and 5. Disposed axially Within the casing is a revoluble center post or stem 6 of heat conductive material which is preferably, though' not necessarily, metallic tubing. The stem 6 is provided 110 with a head 7 preferably of insulating material which is rotatably seated upon the upper shoulder 4 and is provided with a socket 8 within which the upper end of the center post or stem 6 is securely seated. The head 7 is formed with a projecting finger piece 9 engageable alternately with stop lugs 10 upon the casing 1 to limit the to and fro oscillation of the head 7 and stem 6 to a range of approximately ninety degrees.

Surrounding the stem 6 beneath the head 7 is a. helical spring 11, one end of which is secured to the stem, or tothe head by which the stem is carried and the other end of which is secured to the casing. This spring, as will be described, tends to rotate the stem 6 to operate the device from its on to its "oif position.

Fixedly mounted upon the casing or shell in diametrically opposite positions are two electrical contact terminals 12-12. In the present instance these contacts comprise metal strips bent into substantially U formation enclosing the lower margin of the casing or shell with one arm extending interiorly thereof and the other arm extending exteriorly and clenched within the correspondingly positioned slots 3-3. Each contact member 12 is provided with a solder lug or connection 13 to which the electrical circuit lead wires are to be attached.

Mounted upon the stem 6 are two contact arms 14-14 interconnected with each other and adapted upon rocking motion of the stem to make and break contact with the contact terminals 12. In the preferred construction these arms 14 are carried by a metallic thirnble or ilanged collar 15 secured to the stem 6 and electrically connecting the arms to each other.

Secured to the stem 6 by a fusible joint 16 of soft solder, wax, or other adherent heat sensitive material subject to softening by fusing action under increased heat condition, is a detent 17 having arresting engagement with the interior of the casing wall. In the .illustrated construction this detent comprises an extended spring arm 17 having frictional engagement with the interior of the casing wall immediately beneath the shoulder 5 thereby normally not only holding the stem 6 against rotative movement under inuence of the spring l1 but by its engagement beneath the shoulder preventing withdrawal of the head and stem from the casing.

Thestem 6 is turned by the head 7 against the tension ofthe spring 11 to on position wherein the contact arms 14 engage with the contacts l2 to close the electrical circuit, It is held in such position of adjustment by the clutch like engagement of the detent arm 17 with the casing 1 under the inherent tension of such detent arm, thereby maintaining the circuit closed 'A and-the actuating springll under tension.

Varies 18 of heat conductive material are carried at the lower end of the stem and exposed to the temperature of the surrounding atmosphere. The heat absorbed by the vanes 18 being transmitted through the heat conductive stem G to the fusible joint 16 causes the solder, wax or other attachment material to fuse or soften, and its resistance to weaken to suiiicient extent that it is overcome by the tension ofthe spring 11,

' which thereupon actuates the stem and contact arms 14 through a partial rotation to off position breaking the contact between the arms 14 and the contact terminals 12 and opening the electrical circuit.

As the temperature of the surrounding atmosphere decreases, the solder, wax or other uniting material congeals and reunites the detent arm and stem in their newly assumed relation, preparatory to readjustment into on or contacting position.

The temperature at which the joint 16 fuses and releases the stem for action under influence of the spring is determined by the character of the fusible material employed for uniting the parts. Solder may be compounded in varying degrees of hardness from an extremely soft solder, melting at comparatively lowv temperature to hard solders which are heat resistant to a comparatively high degree. By selecting a solder having a fusing point at the temperature at which it is desired that the device shall operate, such operation can be controlled within a relatively narrow range. If operation at lower temperature is desired, wax may be substituted for solder in making the releasable joint 16.

The vanos 18 being heated by contact with surrounding heated atmosphere, the heat is transmitted through the stem to the fusible joint 16, and rwhen the temperature reached the prenined melting point of the solder, the stem released .from the detent 17 by the fusing i the joint 16 and is snapped through decisive rotary motion until arrested by engagement of with it 'the contact arms 14 and thereby openthe circuit. As the temperature of the parts s below the melting point of the solder, the ent arm 17 automatically resolders itself to th center post or stem and the device can be manually reset and the circuit again closed by turning 'the head 7 to "on position. The device cannot be reset, however, until the overheated condition has been corrected and the temperature has again fallen below the melting point oi the solder thus affording positive assurance against continuance of the overheated condition.

The line fuse construction illustrated in Fig. 4 is substantially identical with that heretofore described, except that the casing 1 is completely closed at its lower end which is provided with a contact button or terminal 19 to which is connected one end oi a heater coil 20, The opposite end o t the heater coil 26 attached to one the contact terminals 12. The other terminal 12 is attached to a screw threaded metal jacket 21 exteriorly enclosing the casing 1 and adapted for engagement in a standard fuse plug socket. The heater coil 20, being thus directly included in the electrical circuit, as are also the contact arms 14, becomes heated in event of an overload upon the circuit and the heat generated within the chamber of 'the casing effects release of the fusible joint 16, thereby releasing the stem and contact arms 14 for movement to oil" position under influence of the tensioned spring 1l as before described.

While a spring arm having frictional clutch or braking action upon the interior of the casing is quite effective and practical such detent may be of a pawl and ratchet type as illustrated in Fig. 6 wherein a detent pawl 22 carried by the stem 6 has engagement with ratchet teeth 23 formed interiorly of the casing to hold the stem in its adjusted position against the tension of its spring.

While heretofore described the device is operable under excessive temperature conditions to open the circuit, it will be understood that without any change of construction or operation other than differently positioning the con- Lenders tact arms 14 `upon the stem `v6 whereby they as` sume off positions relative `to the contacts 12` 'an alarm, release a sprinkler system, operate a control device or perform other function.

Therefore such reversely operatingconstruction, which `forms a part-ofthe present invention, shall be 'deemed included within the scope of the hereinafter stated .claims wherein closed position refers tothe operated positionto'which the parts are moved under influence of the spring, and open position refers to the normal position in which the parts are held by the detent against spring tension. From theV above description it will be apparent thatthere is thus provided a device'of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statuter the inventionhas been described fin language more or less specific as to structuralfeatures, itis to be understood that the invention is not liniited to the specific features shownybut that Vthe means and construction herein disclosed comprise the preferred form of` several modes of putting the invention into effect, and the invention is 35` therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims. 4

`Having thus described'my invention, I claim: V1, A resettable fuse, 'including a casing, spaced electrical contacts in thecasing, a rotatable cen,- ter post, diametrically disposed electricalV contacts carried by the post'and moved intoand out of bridging contact with the first mentioned contacts by a partial rotation of thepost, an actuating spring tending torotate the post to rshift the contacts to off position, friction clutch means normally holding the` post and contacts against movement under influence ofthe spring, a fusible connection between` the post` andV clutch adapted to release the post fromthe clutchmeans under influence of abnormal temperature condition,for rotative action to inoperative' position, Said fusible connection being automatically re-establishedin the operated position of the center post to again interconnect the post `and clutch whereby upon returnof the lpost and contacts to their original operative positionsthe clutch will maintain them in such adjusted` position until again released'by fusing 'of the fusible connection. Y

2. In a resettable fuse-plug, a shell-like housing having therein a pair of relatively fixed elec` trical contacts, a movable member within the' housing, a pair of contact members carried there` by and movable into and out of engagement with Ythe electrical contact of said Contact members, a detent normally holding the movable member against movement under influence of the spring,

` a fusible connection between the detent and the movable member automatically released under vinfluence of abnormal temperature conditions tofpermit disengagement of the contacts under influence of the spring, said fusible connection being automatically re-established upon the return `of normal temperature conditions, whereupon the movable memberan'd contact carried therebymay be manually re-adjusted to normal operative position preparatory to subsequent automatic release. i f

3. In a construction of the character described,

a shell-like housing, aicentral rock post therein,

`carried by the post and having operative engage-` ment withr the housing and resisting the actuating influence of the spring, and a fusible joint between-the detent and the post fused by abno'r# mal temperature conditions to disconnect 'the post and vdetent vand permit the post and electrical contact carried thereby to moveto inoperative positionunder influence of the spring, the joint vbetween the post and detent being automatically re-established upon return ofnormal temperature condition.y

4. In a device of the character described, the combination with a make and break electric `switch and actuating means normally tending to open the switch, of a rock stem therefor, a detent arm carried by the stem normally holding the switch against opening movement,"andga fusible joint between the rock stem andthe detent arm adapted to be fused by abnormal temperature 'condition to automatically release the switch for opening action, the joint being automatically re-established upon the return of normal temperature condition preparatoryl to manual re-` setting of the switch in closed condition. v

5. In a device of the character described, the

combination with av make and break electric l.'

switch and actuating means normally tending to open the switch, of a rock stem therefona housing enclosing the operating parts, a detent member having'frictional engagement with the interior wall of the housing to hold the stemand contact against opening movement, a vfusible joint between the detent'member and stern autocrease ofvtemperature thereby permitting rmovement of the' stem and switch to inoperative posiist iii

'matically releasing the Aparts upon abnormal inj tions, the joint being automatically re-established f upon the cooling' of the parts.

6. In a device ofthe` character described, the combination with" a make and breakfelectric switch and actuating. means normally tending to open the switch, a detent member normally connected with the movable element of theswitch.

and operative tc retain the switch in yclosed condition againstr the infiuence of its actuating means, a fusible joint intermediate the detent member and the movable switch element with which the detent is connected, said joint being fused by abnormal increase of temperature to release the switch element for movement to inoperative position said joint being automatically re-established upon the cooling ofthe parts preparatory to succeeding operation and manually operable means for returning the switch to closed condition. Y

7. In a device of the character described, the

combination with a make and break electric switch and actuating means normally tending to open the switch, a detent member normally connected with the movable element of the switch and operative to retain the switch in closed condition against the influence of its actuating means, a fusible joint intermediate the detent member and the movable switch element with which the Ydetent is connected, said joint being fused by abnormal increase of temperature to release the switch element for movement to inoperative position, said joint being automatically re-established upon the cooling of the parts preparatory to succeeding operation, a heat conductive member associated with the fusibly' joined parts kby which the fusible joint is subjected to external temperature conditions, and manually operable Vmeans for returning the switch to closed condition.

8. In a device of the character described, the combination with a make and break electric switch and actuating means normally tending to open the switch, a detent member normally connected with the movable element of the switch and operative to retain the switch in closed condition against the influence of its actuating means, a fusible joint intermediate the detent member and the movable switch element with which the detent is connected, said joint being fused by abnormal increase of temperature to release the switch element for movement to inoperative position, said joint being automatically re-established upon the cooling of the partspreparatory to succeeding operation, a heat transmitting element subjecting the fusible joint to proximate temperature conditions, and manual means for resetting the switch in closed condition.

9. In a device of the character described, the combination with a make and break electric switch and actuating means normally tending to open the switch, a detent member normally connected with the movable element of the switch and operative to retain the switch in closed condition against the influence of its actuating means, a fusible joint intermediate the detent member and the movable switch element with which the ydetent is connected, said joint being fused by abnormal increase of temperature to release the switch element for movement to inoperative position, said joint lbeing automatically re-established upon the cooling of the parts preparatory to succeeding operation, a heat radiating element in proximate relation with the operating parts by which the fusible joint is subjected to increased temperature influence, and manual means for returning the switch to operative position.

l0. In a device of the character described, the

combination with a make and break electric .switch and actuating means normally tending to open the switch, a detent member normally connected with the movable element of the switch and operative to retain the switch in closed condition against the influence of itl actuating means, a fusible joint intermediate the detent member and the movable switch element with which the detent is connected, said vjoint being fused by abnormal increase of temperature to release the switch element for movement to inoperative position, said joint being automatically re-established upon the cooling of the parts preparatory to succeeding operation, :and an electrical heater element in an electrical circuit in which the contacts are connected adapted by its temperature influence to fuse the .joint to release the movable switch element, and manually adjustable means for returning the switch element to its operative position.

11. In a construction of the character described, a make and break electric switch and actuating means tending to open the switch of a housing therefor, a rock stem for the movable switch element, a spring arm carried by the stem having frictional contact with the interior wall of the housing to hold the movable switch element in closed position and a fusible joint between the spring arm and stem automatically releasing the switch element under abnormal increase of temperature, the joint being re-established upon cooling of the parts preparatory to return of the switch element to closed position.

12. In a construction of the character described, a make and break electric switch and actuating means tending to open the switch of a housing therefor, a rock stem for the movable switch element, a detent member having operative engagement with the interior of the housing to maintain the movable switch element in closing position, a fusible joint intermediate the detent and switch element adapted upon abnormal increase of temperature to release the switch element and permit its movement to inoperative position, the joint being automatically re-established upon cooling of the parts preparatory to return of the switch to closed position.

13. In a circuit interrupter, a support, a rotatably mounted member carried in said support and a detent engaging said support and fus'ibly attached to the rotatable member, normally preventing rotation thereof.

14. In a circuit interrupter, a cylindrical support, a member mounted for rotation therein and a member frictionally engaging said support and fusibly. attached to the rst member normally preventing rotation thereof.

EVERETT P. 1 LARSH. 

